A strain of Drosophila melanogaster (SMl/plus l) was replicated into 1000 lines and exposed to chronic low-dose-rate gamma-radiation (7 rads/hours) for 14 generations (a cumulative dose of 33,552 rads). After scoring electrophoretically for mutants at the 7 soluble enzyme loci Got-2, alpha Gpdh, c-Mdh, Adh, Dip-A, Hex-C and alpha Amy, 13 independent mutants were found: 5 at the alpha Gpdh loci, 4 at Hex-C, 2 at c-Mdh, 1 at Got-2 and 1 at Adh. Analysis of the salivary gland chromosomes showed that of these 13 mutants, only 2 (alpha Gpdh) are associated with chromosome aberrations. This shows that at chronic low-dose-rate irradiation the proportion of cytogenetic aberrations is decreasing. An experiment to study the recessive lethal rate induced under chronic low-dose-rate alpha-radiation (7 rads/hours, 14 days, cumulative dose of 2352 rads) showed an induced mutation rate of 3.7 percent for the X-chromosome and 11.7 percent for the second chromosome. This indicates that chronic low-dose-rate alpha-radiation leads to a similar number of mutants/rad as acute irradiation.